It's kind of amazing how quickly things go when you've done them before...
After 3 weeks of getting the first set of walls welded in and pressure tested, it took me just under two days to get the final set put in place. I spent considerable time leak/pressure testing the first set to make 100% certain no fuel would leach into the oil portion of the tank. Turns out, the trickiest part was at the bottom folded edge of the stock tank. When it's stamped from the factory, a tiny tiny channel is created that runs the perimeter of the tank completely preventing you from sealing it off unless you cut it and weld it from the edge.
Ignoring my wonderful weld blowout, I had to cut through the entire edge of the tank to seal it off from the larger section.
I made a little seal that fits into the filler neck where I pressurized the tank to 2-3 psi and sprayed soapy water all over the tank to look for bubbles, found quite a few:
Once all the leaks were stopped up, I started on the second set of walls so that no hot oil surface is ever in direct contact with a surface that holds gas. This should help reduce the amount of heat transfer between hot oil and gas but it's not going to be perfect. I've been using a contour gauge to help me match the surfaces, creating a cardboard pattern then slowly building it up piece by piece. The process worked out much better the second time around as I had the first wall to guide me.
So a day after starting, I finished the welds (brazes, whatever) and pressure tested again. I drilled a small hole between the first and second sets of walls so that I could pressurize the tiny area between the two walls to ensure the 2nd set was leak proof.
Now the actual fun part begins, welding in parts from the stock tank I chopped up literally 6 years ago. Drain plug, send and return. Not shown is the air/oil separator but that'll go in as well. The trick will be getting the tank to vent properly but I think it's possible.
